Spinning, processing, and applications of carbon nanotube filaments, ribbons, and yarns

ABSTRACT

Coagulation spinning produces structures such as fibers, ribbons, and yarns of carbon nanotubes. Stabilization, orientation, and shaping of spun materials are achieved by post-spinning processes. Advantages include the elimination of core-sheath effects due to carbonaceous contaminants, increasing mechanical properties, and eliminating dimensional instabilities in liquid electrolytes that previously prohibited the application of these spun materials in electrochemical devices. These advances enable the application of coagulation-spun carbon nanotube fibers, ribbons, and yarns in actuators, supercapacitors, and in devices for electrical energy harvesting.

[0001] This invention was made with Government support under ContractNo. MDA972-00-C-0032 awarded by the Defense Advanced Projects Agency.The Government has certain rights in this invention.

[0002] This application claims priority on provisional Application Ser.No. 60/245,161 filed on Nov. 3, 2000, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] Methods are described for spinning fibers, ribbons, and yarnscomprised of carbon nanotubes; the stabilization, orientation, andshaping of spun materials by post-spinning processes; and theapplication of such materials made by spinning.

[0005] 2. Description of the Related Art

[0006] Since the discovery of carbon nanotubes by Iijima and coworkers(Nature 354, 56-58, (1991) and Nature 361, 603-605 (1993)) various typesof carbon nanotubes (NTs) have been synthesized. A single-wall carbonnanotube (SWNT) consists of a single layer of graphite that has beenwound into a seamless tube having a nanoscale diameter. A multi-wallcarbon nanotube (MWNT), on the other hand, comprises two or more suchcylindrical graphite layers that are coaxial. Both single-wall andmulti-wall nanotubes have been obtained using various synthetic routes,which typically involve the use of metallic catalysts and very highprocessing temperatures. Typical synthesis routes are those employing acarbon arc, laser evaporation of carbon targets, and chemical vapordeposition (CVD).

[0007] SWNTs are produced by the carbon-arc discharge technique using apure carbon cathode and a carbon anode containing a mixture of graphitepowder and catalytic metal(s), like Fe, Ni, Co and Cu (D. S. Bethune etal. Nature 363, 605-7 (1993) and S. Iijima and T. Ichihashi, Nature 363,603-5 (1993)). C. Journet et al. (Nature 388, 756-758 (1997)) havedescribed an improved carbon-arc method for the synthesis of SWNTs whichuses Ni/Y (4.2/1 atom %) as the catalyst. Co-vaporization of carbon andthe metal catalyst in the arc generator produced a web-like deposit ofSWNTs that is intimately mixed with fullerene-containing soot.

[0008] Smalley's group (A. Thess et al., Science 273, 483-487(1996))developed a pulsed laser vaporization technique for synthesis of SWNTbundles from a carbon target containing 1 to 2% (w/w) Ni/Co. The duallaser synthesis, purification and processing of single-wall nanotubeshas been described in the following references: J. Liu et al., Science280, 1253 (1998); A. G. Rinzler et al., Applied Physics A 67, 29 (1998);A. G. Rinzler et al., Science 269, 1550 (1995); and H. Dai, et al.,Nature 384, 147 (1996).

[0009] The CVD method described by Cheng et al. (Appl. Phys. Lett. 72,3282 (1998)) involves the pyrolysis of a mixture of benzene with 1 to 5% thiophene or methane, using ferrocene as a floating catalyst and 10%hydrogen in argon as the carrier gas. The nanotubes form in the reactionzone of a cylindrical furnace held at 1100-1200° C. Depending on thethiophene concentration, the nanotubes form as either multi-wallnanotubes or bundles of single-wall nanotubes. Another useful method forgrowing single-wall nanotubes uses methane as the precursor, ferricnitrate contained on an alumina catalyst bed, and a reaction temperatureof 1000° C.

[0010] Another CVD synthesis process was described by R. E. Smalley etal. in PCT International Application No. WO 99-US25702, WO 99-US21367and by P. Nikolaev et al. in Chem. Phys. Lett. 313, 91-97 (1999). Thisprocess, known as the HiPco process, utilizes high pressure (typically10-100 atm) carbon monoxide gas as the carbon source, and nanometersized metal particles (formed in-situ within the gas stream fromorgano-metallic precursors) to catalyze the growth of single-wall carbonnanotubes. The preferred catalyst precursors are iron carbonyl (Fe(CO)₅)and mixtures of iron carbonyl and nickel carbonyl (Ni(CO)₄). The HiPcoprocess produces a SWNT product that is essentially free of carbonaceousimpurities, which are the major component of the laser-evaporation andcarbon-arc products. The process enables control of the range ofnanotube diameters produced, by controlling the nucleation and size ofthe metal cluster catalyst particles. In this way, it is possible toproduce unusually small nanotube diameters, about 0.6 to 0.9 nm.Finally, the HiPco process is scalable to low cost tonnage productionand is not nearly as energy intensive as the laser evaporation andcarbon-arc processes.

[0011] The nanotube-containing products of the laser-evaporation andcarbon-arc processes invariably contain a variety of carbonaceousimpurities, including various fullerenes and less ordered forms ofcarbon soot. The carbonaceous impurity content in the raw products ofthe laser and carbon arc processes typically exceeds 50 weight %.Purification of these products generally relies on selective dissolutionof the catalyst metals and highly ordered carbon clusters (calledfullerenes) followed by selective oxidation of the less orderedcarbonaceous impurities. A typical purification process is described byLui et al. in Science 280, 1253 (1998). This method involves refluxingthe crude product in 2.6 M nitric acid for 45 hours, suspending thenanotubes in pH 10 NaOH aqueous solution using a surfactant (e.g.,Triton X-100 from Aldrich, Milwaukee, Wis.), followed by filtrationusing a cross-flow filtration system. While the effects of thesepurification processes on the nanotubes themselves are not completelyunderstood, it is believed that the nanotubes are shortened byoxidation.

[0012] As discussed by B. I. Jakobson and R. E. Smalley (AmericanScientist 85, 325, 1997) SWNT and MWNT materials are promising for awide variety of potential applications because of the exceptionalphysical and chemical properties exhibited by the individual nanotubesor nanotube bundles. Some SWNT properties of particular relevanceinclude metallic and semiconducting electrical conductivity, dependingon the specific molecular structure, extensional elastic modulus of 0.6TPa or higher, tensile strengths on the order of ten to one hundred GPa,and surface areas that can exceed 300 m²/g.

[0013] The proposed applications of carbon nanotubes include mechanicalapplications, such as in high-strength composites, electricalapplications, and multifunctional applications in which differentproperties aspects of the carbon nanotubes are simultaneously utilized.Tennent et al. in U.S. Pat. No. 6,031,711 describe the application ofsheets of carbon nanotubes as high performance supercapacitors. In thisapplication, a voltage difference is applied to two high-surface-areacarbon nanotube electrodes that are immersed in a solid or liquidelectrolyte. Current flows in the charging circuit, thereby injectingcharge in the nanotubes, by creating an electrostatic double layer nearthe nanotube surfaces.

[0014] The application of carbon nanotube sheets as electromechanicalactuators has been recently described (R. H. Baughman et al., Science284, 1340 (1999)). These actuators utilize dimension changes that resultfrom the double-layer electrochemical charge injection intohigh-surface-area carbon nanotube electrodes. If carbon nanotubes can beassembled into high modulus and high strength assemblies (such asfilaments, ribbons, yams, or sheets) that maintain their ability toelectrochemically store charge, then superior actuator performanceshould be obtainable. The problem has been that no methods are presentlyavailable for the manufacture of nanotube articles that have theseneeded characteristics.

[0015] These and other promising applications require assembling theindividual nanotubes into macroscopic arrays that effectively use theattractive properties of the individual nanotubes. This obstacle has sofar hindered applications development. The problem is that MWNTs andSWNTs are insoluble in ordinary aqueous solvents and do not form meltseven at very high temperatures. Under certain conditions, and with theaid of surfactants and ultrasonic dispersion, bundles of SWNTs can bemade to form a stable colloidal suspension in an aqueous medium.Filtration of these suspensions on a fine-pore filter medium, asdescribed by Lui et al. in Science 280, 1253 (1998), results in theproduction of a paper-like sheet which has been called “bucky paper” (inreference to buckminsterfullerene, or C₆₀, the first member of thefullerene family of carbon cluster molecules). Such sheets, which canrange in conveniently obtainable thickness from 10-100 microns, possessmechanical strength derived from the micro-scale entanglement of thenanotube bundles. Bucky paper preserves the large accessible surfacearea of the nanotube bundles, but typically exhibit greatly reducedelastic modulus values (a few GPa) that are a very small fraction of theintrinsic elastic modulus of either the individual SWNTs or the SWNTbundles.

[0016] A recently reported method for processing carbon nanotubesprovides nanotube fibers whose mechanical properties significantlysurpassing those of ordinary bucky paper. This method was described byP. Bernier et al. (talk Tue E1 at the International Conference onScience and Technology of Synthetic Metals, Gastein, Austria, Jul.15-21, 2000). According to this process, the carbon nanotubes are firstdispersed in an aqueous or non-aqueous solvent with the aid of asurfactant. A narrow jet of this nanotube dispersion is then injectedinto a rotating bath of a more viscous liquid in such a way that shearforces at the point of injection cause partial aggregation and alignmentof the dispersed nanotube bundles. This viscous liquid contains an agentor agents, which act to neutralize the dispersing action of thesurfactant. Consequently, the jet of dispersed nanotubes is rapidlycoagulated into a low-density array of entangled nanotubes—therebygaining a small (but useful) amount of tensile strength. The wetfilament is then washed in water, and the washed filament issubsequently withdrawn from the wash bath and dried. During whichdraw-dry process, capillary forces collapse the loosely tangled array ofnanotubes into a compact thin fiber having a density of about 1.5 gm/cc(close to the theoretical density of a compact array of carbonnanotubes). This total process will henceforth be referred to as thecoagulation spinning (CS) process.

[0017] In a typical coagulation spinning process, as described byBernier et al. (talk Tue E1 at the International Conference on Scienceand Technology of Synthetic Metals, Gastein, Austria, Jul. 15-21, 2000),the nanotubes are dispersed in water with the aid of sodium dodecylsulphate (SDS) surfactant. The viscous carrier liquid is an aqueoussolution of polyvinyl alcohol (PVA) in which the PVA also serves toneutralize the effect of the SDS surfactant by directly replacing thesemolecules on the NT surfaces. Bernier et al. describe preferredconcentrations for the various ingredients, and viscosity ranges andflow velocities of the spinning solutions. Polarized light microscopy ofthe coagulated nanotube fibers confirms preferential alignment of theNTs along the fiber axis. Further evidence of NT alignment is providedby the measured extensional elastic modulus, which is approximately 10GPa for the final CS fibers, as compared to typically 1 GPa for buckypaper.

[0018] Unfortunately, the fibers made by the CS process are not usefulin applications as electrodes immersed in liquid electrolytes because ofa surprising shape memory effect. This shape memory effect causes the CSfibers to dramatically swell (by 100% or more) and lose most of theirdry-state modulus and strength. Because of this structural instabilityof fibers made by the CS process, they are unusable for criticallyimportant applications that use liquid electrolytes, such as insupercapacitors and in electromechanical actuators. In contrast,as-produced bucky paper made from the same nanotubes can be used forboth capacitor and actuator devices that use liquid electrolytes.

[0019] Another drawback of the current CS process is that it has beensuccessfully applied only for nanotube-containing samples that containan enormous amount of carbonaceous impurities (about 50% by weight ormore). Practice of this CS process with purified nanotubes has beenuniversally unsuccessful, which has suggested that the carbonaceousimpurities might be playing an important role in the initial stage ofthe CS spinning process. Because of the presence of these impurities,the as-spun carbon nanotubes fibers contain about 50 volume percent ofcarbonaceous impurities, which degrade mechanical and electronicproperties. In addition, since the CS process does not enable asubstantial mechanical draw, the obtained modulus of the fibers madethis process is 15 GPa or less, which is over an order of magnitudelower than that of the constituent nanotubes (about 640 GPa).

SUMMARY OF THE INVENTION

[0020] As has been shown, the coagulation spinning (CS) process of theconventional art has disadvantages which prevent the utilization ofcarbon nanotube structures as electrode materials. The conventional artprocess could not be successfully applied to carbon nanotubes that aresubstantially free of carbonaceous impurities. The conventional artprocess was unstable since it could be practiced only in a narrow rangeof spinning parameters and a very restricted concentration range for thecarbon nanotubes in the spinning solution. The degree of alignment ofthe fibers produced by the conventional art CS process is not high.Also, the nanotube fibers spun by the conventional art are notdimensionally stable and the mechanical properties degrade when thesefibers are placed in liquid electrolytes for electrochemicalapplications.

[0021] An advantage of this invention, in part, is that it eliminatesthe deficiencies in the conventional coagulation spinning (CS) processand in the properties of these conventional spun materials. Two criticaldeficiencies are (1) the need to conduct CS spinning with highly impurematerial that typically contains over 50% by weight carbonaceousimpurities that are intimately mixed with the carbon nanotubes and (2)the dimensional and mechanical instability of materials spun by the CSmethod in the liquid electrolytes that are used for importantapplications.

[0022] A further advantage of this invention, in part, is that itenables the continuous, high-throughput spinning of structures such asfibers, ribbons, and yarn. Yet another advantage of this invention isthat it improves the mechanical properties of spun materials byproviding means to increase the draw ratio of materials produced by theCS approach.

[0023] A further advantage of this invention, in part, is that itprovides means for the production of CS derived materials in the formsthat are most useful for particular applications.

[0024] The invention, in part, provides a coagulation spun structurecontaining single-wall carbon nanotubes, the structure swelling by lessthan 10% in diameter when immersed in water.

[0025] The invention, in part, provides fiber, ribbon or yarn havinggreater than about 90 weight percent carbon single-wall nanotubes,wherein the average diameter of the single wall carbon nanotubes rangesfrom about 0.6 to 0.9 nm. The invention, in part, also provides a fiberof single-wall carbon nanotubes that contain no binding agents orcarbonaceous impurities.

[0026] The invention, also in part, provides a process for making astructure containing carbon nanotubes that entails forming a uniformsuspension of carbon nanotubes in a liquid, coagulation spinning thesuspension to form the structure, and annealing the structure atannealing temperatures sufficient to stabilize the structure againswelling and loss of mechanical strength upon emersion in water oranother liquid.

[0027] The invention, also in part, provides a process of coagulationspinning of a fiber ribbon or yam that entails providing a first liquidcomprising a uniform dispersion of single wall carbon nanotubes, andinjecting the first liquid as a jet into a second coagulation liquid,the jet being formed in an orifice of decreasing diameter that creates aconverting flow field at close to the point of injection into the secondcoagulation liquid.

[0028] Advantages of the present invention will become more apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be more clearly understood and furtherapplications will be apparent when reference is made to the followingdetailed description of preferred embodiments of the invention which aregiven by way of illustration only, and thus are not limitative of thepresent invention, and wherein:

[0030]FIG. 1 shows the molecular structures of (6,6) and (10,10) carbonnanotubes.

[0031]FIG. 2a shows plots of actuator strain for an thermally annealedcoagulation-spun SWNT fiber in 1 molar NaCl aqueous solution. FIG. 2bshows the generated stress versus the peak-to-peak of the appliedvoltage.

[0032]FIG. 3 shows compositions of spinable inks and gels in thewater/carbon nanotube/sodium dodecyl sulphate system.

[0033]FIG. 4 shows two shear-flow injection nozzles for the coagulationspinning process, a variable-shear-rate design with a conicalcross-section, and a constant-shear design with a paraboliccross-section.

[0034]FIG. 5 shows a coaxial pure extensional flow nozzle for thecoagulation spinning process.

[0035]FIG. 6 shows a concentrating nozzle for removing excess carrierliquid in the coagulation spinning process.

[0036]FIG. 7 shows the extensional flow nozzle of FIG. 5 combined withthe shear flow nozzle of FIG. 5.

[0037]FIG. 8 shows a flow junction for combining multiple filaments inthe coagulation spinning process.

[0038]FIG. 9 shows a schematic of a double-layer chargeelectromechanical actuator that also functions as a supercapacitor.

[0039]FIG. 10 shows a schematic of a woven article comprising ribbons ofaligned carbon nanotubes produced by the improved coagulation spinningprocess and stabilized by heat treatment.

[0040]FIG. 11 shows a schematic of a wound article comprising ribbons ofaligned carbon nanotubes produced by the improved coagulation spinningprocess and stabilized by heat treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The coagulation spinning (CS) process of the conventional art hasthe following liabilities that are eliminated by the present invention:(a) the conventional art process could not be successfully applied tocarbon nanotubes that are substantially free of carbonaceous impurities,(b) the conventional art process was unstable since it could bepracticed only in a narrow range of spinning parameters and a veryrestricted concentration range for the carbon nanotubes in the spinningsolution, (c) the degree of alignment of the fibers produced by theconventional art CS process is not high, and (d) the nanotube fibersspun by the conventional art are not dimensionally stable and themechanical properties degrade when these fibers are placed in the liquidelectrolytes that are needed for key applications.

[0042] The invention overcomes the difficulties associated with CSprocess described by P. Bernier et al. (Talk Tue E1 at the InternationalConference on Science and Technology of Synthetic Metals, Gastein,Austria, Jul. 15-21, 2000). According to this process, the carbonnanotubes are first dispersed in an aqueous or non-aqueous solvent withthe aid of a surfactant. A narrow jet of this nanotube dispersion isthen injected into a flowing stream of a more viscous carrier liquid insuch a way that shear forces at the point of injection cause partialaggregation and alignment of the dispersed nanotube bundles. The viscouscarrier liquid also contains an agent or agents, which act to neutralizethe dispersing action of the surfactant. Consequently, the jet ofdispersed nanotubes is rapidly coagulated into a low-density array ofentangled nanotubes—thereby gaining a small but useful amount of tensilestrength. The wet filament is then washed in water, and the washedfilament is subsequently withdrawn from the wash bath as it is dried.

[0043] In a typical conventional coagulation spinning process, describedby Bernier et al. at the above conference, the nanotubes are dispersedas a substantially uniform suspension in water with the aid of sodiumdodecyl sulphate (SDS) surfactant. The viscous carrier liquid is anaqueous solution of poly(vinyl alcohol) (PVA) in which the PVA serves toneutralize the effect of the SDS surfactant by directly replacing theSDS molecules on the NT surfaces. These nanotube dispersions wereinjected as a liquid jet into a rotating bath of an aqueous solution ofPVA using a syringe pump and a capillary tube immersed in the PVAsolution. Under favorable conditions, the nanotube solution formed acontinuous ribbon as a spiral inside the PVA solution. Bernier et al.mention preferred concentrations for the various ingredients, andviscosity ranges and flow velocities of the spinning solutions. Theribbon was subsequently washed in water and dried in air during drawingfrom an aqueous bath to form nanotube filaments.

[0044] The initial attempts to improve the CS process focused onreplacing the unpurified nanotube soot with chemically purifiedarc-produced or laser-produced nanotubes. The results of Examples 2-4,indicate that impurities in the nanotubes might be serving as essentialbinding agents at the junctions between nanotubes during the criticallyimportant coagulation stage of spinning. The liquid jet containingchemically purified carbon nanotubes either broke into short segmentsduring injection of the liquid jet into the carrier liquid or formedpoorly structured ribbons that were too weak to remove from the washbath.

[0045] In contrast with the applicability of the CS process forunpurified carbon-arc-produced SWNT samples containing about 50% byweight carbonaceous impurities, the results of Example 2 show that thechemically purified arc-produced SWNTs could not be spun. In addition,Example 3 shows that purified SWNTs obtained by chemically purifying theproduct of the laser evaporation method (J. Lui et al., Science 280,1253 (1998)) could also not be spun by the CS process. Likewise, Example4 shows that purified SWNT samples could not be spun that were derivedby chemically purifying the reaction product of the decomposition ofmethane over a catalyst-containing zeolite.

[0046] While all of the above described attempts to spin fibers ofchemically purified nanotubes by the CS process failed, we weresurprisingly successful in spinning high purity SWNT produced by thecarbon monoxide process (HiPco). These nanotube fibers, which havenarrow diameters (about 0.8 nm) and long bundle lengths, spin over amuch broader concentration range than the unpurified arc-producednanotube soot, and produce mechanically robust fibers that are easilydrawn from the coagulation bath. While CS fibers made using unpurifiednanotube soot contain a nanotube-rich core surrounded by a thick crustof carbonaceous impurities, the HiPco CS fibers of the invention arefree of crust and consist almost entirely of carbon nanotubes. Thissurprising success is described in Examples 1 and 5.

[0047] The preferred nanotubes made by the high pressuredisproportionation of carbon monoxide can have a smaller diameter, inthe range 0.6 nm to 0.9 nm, than those made by the laser evaporation orcarbon arc processes, which typically produce nanotubes with diametersgreater than 1 nm. The most preferred nanotubes for coagulation spinningare made by the HiPco process at high pressure (typically 30-50atmosphere), at high temperatures (typically 900-1100° C.), and using aniron containing catalyst. To illustrate the difference, FIG. 1 shows a(6,6) nanotube with a diameter of about 0.6 nm, a structure which may bepresent at high concentrations in the HiPco product, contrasted with a(10,10) nanotube with a diameter of about 1.4 nm. The (10,10) nanotubeis one of many structures of larger diameter, which typically comprisethe products of the laser evaporation and carbon arc processes. Webelieve that the small diameter of the HiPco nanotubes contributes,along with the freedom from carbonaceous impurities, to the robustnessof the coagulation-spun fibers, ribbons and yams. The uniqueness of theHiPco material of the invention is demonstrated by the Examples 2-4,which show that chemically purified arc-produced nanotubes, chemicallypurified laser-produced nanotubes, and chemically purifiedzeolite-produced nanotubes are unsatisfactory for processing by thecoagulation spinning process.

[0048] The present discovery that high purity, small-diameter HiPcoSWNTs can be spun by CS provides an opportunity to engineer theproperties of CS spun structures such as fibers, ribbons, and yams. Thistechnology can also be utilized to form structures such as sheets,tapes, mats, threads, tubes, ropes, twines, braids and cords. Forexample, in order to increase the area of nanotube surface exposed toelectrolyte for electrochemical applications, one can use thecoagulation spinning process to create fibers, ribbons, and yarnscomprising a mixture of HiPco and other single-wall or multi-wallnanotubes such that the diameter distribution of the nanotubes is atleast bimodal with one peak centered in the range of 0.6 nm to 0.9 nmand one or more other peaks at a larger diameters in the range of about1.0 nm to about 2.0 nm. In this case the tendency of the nanotubes toform well-ordered bundle structures is partially disrupted and moresurface area is available for contact with the electrolyte. While narrowdiameter carbon nanotubes prepared by the high pressure carbon monoxideprocess are most preferred for invention embodiments, various knownmethods (W. K. Hsu, Chem. Phys. Lett. 323, 572-579 (2000)) can be usedto add a significant amount of boron or nitrogen to carbon nanotubes andthese boron or nitrogen containing nanotubes are within the preferredrange of compositions for invention embodiments.

[0049] An important additional advantage of using HiPco nanotubes incoagulation spinning is that the range of spinable NT suspensioncompositions in the water-nanotube-sodium dodecyl sulphate (SDS) systemis expanded to a wider range of NT concentrations and to a wider rangeof SDS concentrations than in the known CS process using impurecarbon-arc-produced NTs. This is illustrated in FIG. 3 which shows thataqueous suspensions of HiPco nanotubes containing up to 0.5 wt. % NTsand up to 3 wt. % SDS can be spun into continuous fibers. The increasedNT concentrations in these HiPco nanotube suspensions are advantageousin that they lead to stronger more easily processed filaments in the wetstate.

[0050] The invention is not restricted to spinning nanotube dispersionsthat use sodium dodecyl sulphate as a surfactant. Other sodium alkylsulfates can be used in the range of sodium C₈—C₃₀ alkyl sulphate.Examples of these sodium alkyl sulphates include sodium nonyl sulphate,sodium decyl sulphate, sodium undecyl sulphate, sodium tetradecylsulphate, sodium hexadecyl sulphate, sodium lauryl sulphate, sodiumstearyl sulfate and sodium cetyl sulphate. Sodium alkyl sulfates basedupon coconut oil, tallow or tall oil may be used. Besides the anionicsurfactants, cationic and nonionic surfactants can be used. Cationicsurfactants include alkylpyridinium halides and quaternary ammoniumsalts such as dialkyldimethylammonium salts, alkylbenzyldimethylammoniumchlorides, alkyltrimethylammonium salts. Nonionic surfactants includepolyoxyethylene surfactants, alkylphenol ethoxylates, carboxylic acidesters, glycerol esters, anhydrosorbitol esters, ethoxylated fats, oilsand waxes, and glycol esters of fatty acids. Mixtures of surfactants canalso be used. In certain cases, like the coagulation spinning of carbonnanotubes from dispersions in organic liquids or the spinning ofpolymer-coated nanotubes from organic liquids, it is not necessary touse a surfactant in the spinning solution. Examples of organic liquidsare toluene, xylene, and related aromatics, alcohols, glycols, C₈—C₃₀hydrocarbons, esters such as ethyl acetate, ketones, dimethylsulfoxideand dimethylformamide.

[0051]FIG. 3 also shows two aqueous compositions at 1.2 wt. % SDS-0.8%NTs and at 2.0 wt. % SDS-0.7% NTs that form homogeneous spinable gelsafter sonication. By a gel we mean a semi-solid material which is quitesoft but which will maintain its shape and not spontaneously flow like aliquid under arbitrarily small forces. This gel will not flow easilythrough the narrow capillary channel used in the known coagulationspinning process, but it can be forced by higher pressures to flowthrough a larger diameter feed tube and thence through an orifice of thetype shown in FIG. 4, from which it is injected into a moving carrierbath. A major degree of nanotube orientation into directions parallel tothe flow streamlines occurs as the gel is extruded through the shearflow region in the orifice, and the new oriented juxtaposition of thenanotubes is temporarily fixed by the gel's resistance to flow. In thiscase, the viscosity of the carrier bath is less important than in thecase where the injected nanotube solution is a liquid. The coagulationaction of the carrier bath does not have to be as strong since the gelhas some strength, which preserves the extruded shape after ejectioninto the carrier bath. In addition, the spinable aqueous NT-SDS gels canbe spun into non-aqueous polar solvents such as alcohols or glycolswhich rapidly extract the water from the injected NT jet, therebyproducing a more robust filament which can be drawn in the wet state toimprove NT alignment.

[0052] Our efforts to use the long SWNT fibers produced by the CSprocess showed these fibers were useless for applications that useexpose these fibers to a liquid electrolyte—such as inliquid-electrolyte-based energy storage, actuator, and energy harvestingdevices. More specifically, fibers made by this process swell indiameter by up to 300% when immersed in water or an aqueous electrolyte,and dramatically decrease both modulus and strength. It appears thatinter-bundle stress transfer within the fibers is facilitated byresidual polymer from the spinning bath (such as PVA). Immersion in anaqueous solution apparently transforms this residual polymer into a gelhaving little binding capability, causing a shape memory effect in whichthe fibers partially expand to distantly approach the post-coagulation,pre-dried state.

[0053] Fortunately, we discovered (Example 6) that this degradationcould be eliminated by simply annealing the as-spun fibers (for example,at 250° C. for one hour in dynamic vacuum). Thereafter, the carbonnanotube fibers preformed well as electromechanical actuators, as shownin Example 7. The times and temperatures that are preferably utilizedare interrelated, since a thermal exposure at high temperature and shorttimes can have the equivalent effect of thermal exposure at a lowertemperature for shorter times. The preferable temperatures range fromabout 200° C. to about 2100° C. More preferably, this temperature rangeis about 400° C. to about 1200° C. In these lower limits, the timesutilized have no upper limit, but the preferred lower limit on theannealing time is about 20 minutes. At the highest temperature, thepreferred annealing time is in milliseconds or sub-milliseconds. At thelower annealing temperatures the annealing process can be optionallyconducted in air. However, at long annealing times at temperatures aboveabout 600° C. it is preferable that the annealing be conducted in aninert atmosphere or in a reducing atmosphere, such as hydrogen.

[0054] In addition, long residence times at temperatures of higher thanabout 1500° C. can cause the growth of nanotube diameters by inter-tubecoalescence. Similarly, long residence times at above 2000° C. areusually undesirable, since substantial exposure at these temperaturescan convert SWNTs to MWNTs. One skilled in the art can determine theoptimal residence time at a particular temperature or combination oftemperatures by using thermogravimetric analysis to characterize thethermal exposure required to substantially remove any bonding agent(such as PVA) that degrades mechanical properties by losing mechanicalstrength in an aqueous electrolyte. This combination of annealing timesand temperatures should preferably reduce the diameter swelling of thenanotube fiber when immersed in water to less than 10%. More preferably,the swelling in nanotube diameter should be negligible when the nanotubeis immersed in any electrolyte used for devices.

[0055] Annealing carbon nanotube fibers under a state of tension,applied especially during the lower temperature stages of the annealingprocess, can be used to increase the elastic modulus of the material inthe annealed state. Such annealing processes, with and without appliedtensile forces, can also be applied to woven or wound structurescomprising carbon nanotube fibers, ribbons or yarns produced by thecoagulation spinning process. In one preferred annealing processes, thefiber, ribbon or yarn is treated under a state of tension in anatmosphere of steam as the temperature is raised from ambient to about400° C. The steam acts to soften residual polymeric material in thefiber and facilitate nanotube alignment during stretching. Optionally,the atmosphere can be then changed to an inert atmosphere, such as highpurity argon or nitrogen, or vacuum, and the temperature can beincreased to about 1100° C. while the tension is maintained. The tensilestress in the fiber, ribbon, or yarn is preferably maintained in a rangeof between about 10 MPa and about 300 MPa and more preferably betweenabout 50 MPa and about 200 MPa during annealing. As an alternativepreferred method, the carbon nanotube fiber, ribbon, or yarn can be heldat substantially constant length during the annealing process. Becausethe carbon nanotubes can be readily oxidized at temperatures in excessof 600° C., annealing at these temperatures is preferably accomplishedin either an inert or reducing atmosphere.

[0056] Additionally, the invention provides methods for improving uponthe known coagulation spinning process to increase nanotube alignmentand to transform this semicontinuous or batch process to a continuousprocess. FIG. 4 shows schematic drawings of two shear-flow-inducingspinnerets or nozzles for creating alignment of the suspended nanotubearrays prior to injection into the coagulation bath. The use ofshear-flow-inducing spinnerets or nozzles of this general design is wellknown in the art of spinning dissolved or molten polymers, but isunknown and undemonstrated for spinning of fibers from a colloidalsuspension. A. G. Ferrari in U.S. Pat. No. 3,382,535 describes thedesign principles for this type of spinning nozzle. H. L LaNieve in U.S.Pat. No. 4,015,924 describes a formula for a capillary profile toestablish an essentially constant extensional strain rate condition forflow of liquid. Both nozzles shown in FIG. 4 are characterized by asection of decreasing diameter immediately upstream from the injectionorifice. In both cases, a nozzle body 1 conducts a flow of the nanotubesuspension 2 through a converging flow field 3 and 4, after which a jetof nanotube suspension 5 is injected into the coagulation bath (notshown). In the constant-shear-rate nozzle, the converging flow section 4is parabolic in shape. The simple conical converging flow section 3 ofthe variable shear nozzle is easier to manufacture and is especiallypreferred for coagulation spinning applications. In both of thesenozzles the inlet diameter is preferably in the range of from about 0.5mm to about 5 mm and more preferably in the range of from about 1 mm toabout 3 mm while the minimum diameter of the jet at the outlet ispreferably in the range of from 0.01 mm to about 1 mm and morepreferably in the range of from about 0.05 mm to about 0.2 mm.Similarly, for both designs, the ratio of the cross-sectional area ofthe entrance flow field to that of the exit flow field is preferably inthe range of from about 5 to about 1000 and more preferably in the rangeof from about 10 to about 100. Both of these designs are effective atflow alignment of the NTs near the center of the NT suspension jet, butalignment is less effective near the perimeter of the jet due toboundary layer constraints.

[0057] The advantage of this shear flow injection nozzle over theunconstrained jet injection method of the known CS process is that usingthe shear flow nozzle allows a significant increase in the intensity ofthe extensional flow in the NT suspension with an accompanying increasein the degree of NT alignment in the resulting fibers and ribbons. Thenozzle geometries shown in FIG. 4 can be used to spin either liquid,gel, or semisolid carbon nanotube suspensions.

[0058] In the example shown in FIG. 4, the cross-sections of the inletand outlet flows are round. However, shaped fibers can be created byappropriately shaping the outlet orifice. In the simplest case, an ovalor rectangular ribbon cross-section can be made in this way but it isalso possible to create fibers with a wide range of multi-lobedcross-sections which are substantially non-round, non-elliptical,non-oval, and non-rectangular in shape. This family of shaped fibercross-sections includes but is not limited to star shapes, cross shapes,Maltese cross shapes and the like. Such shaped NT fibers are useful inthe construction of electrochemical carbon nanotube materials anddevices for minimizing the time for diffusion of ions from anelectrolyte to NTs in the interior of a fiber, while retaining the fulltensile properties of NTs oriented in the fiber direction.

[0059]FIG. 5 shows schematically a contained flow variant of thecoagulation spinning process in which the nanotube suspension 6 and thecarrier phase 7 are simultaneously introduced into a contained entranceflow field 8 and subsequently pass through a contained extensional flowfield 9 and a contained exit flow field 10. In this case, the boundaryof the NT suspension jet is unconstrained as it passes through thecontained extensional flow field, resulting in nearly pure extensionalflow in this region across the entire diameter of the jet. All flowstreamlines 11, which enter the entrance flow field on the left will befound to leave through the exit flow field on the right. The variousflow field dimensions and area ratios in this design are the same asquoted above for the nozzle designs shown in FIG. 4. The advantages ofthis process variant include full control over the extensional reductionin area leading to maximum NT alignment. In addition, this processvariant captures the newly formed coagulated wet NT filament in acontained flow convenient for application of the subsequent processsteps illustrated in FIGS. 6 and 7.

[0060]FIG. 6 shows a schematic of a concentrating nozzle which acceptsthe output of the nozzle of FIG. 5 including the coagulated NT filament6 (of the nanotube suspension) and the coagulating liquid stream 7 (ofthe carrier phase). An impervious wall 12 bound the entrance flow fieldof this nozzle. The concentrating flow field, however is bounded by aporous wall 13, through which a metered amount of coagulating liquidexits into a surrounding plenum 14 from which it can be recycled to theupstream stages of the process. The exit flow field 15 now contains thecoagulated filament 6 and a much-reduced flow of coagulating liquid. Thedimension of this nozzle and exit flow rate of coagulating liquid arepreferably selected so as to remove preferably at least 80% and morepreferably at least 95% of the coagulating liquid. A positivedisplacement pump, such as a gear pump controls the volume flow rate ofthe exiting coagulation liquid. The coagulated wet NT filament nowpasses out of the exit flow field surrounded by a thin layer ofcoagulating liquid which serves to lubricate and protect the filamentfrom disruption by velocity gradients in the boundary layer near theexit flow field wall.

[0061]FIG. 7 shows a combination of the shear flow nozzle of FIG. 4combined with the coaxial extension flow nozzle of FIG. 5. In this case,the nanotube suspension 25 and the PVA phase 26 are introduced into theflow field so that the NT filament 28 exits the nozzle while theeffluent PVA 27 exits the sides.

[0062]FIG. 8 shows schematically a combination of the aligning nozzles16 and the concentrating nozzles 17 wherein the aligning nozzle exitflow field and stream dimensions are identical to the input flow fieldand stream dimensions of the concentrating nozzles. Some distancebetween the two nozzles is required to allow sufficient time for thefull coagulation of the NT filament. This distance depends on thediameter of the NT filament and the flow velocity. In general, thedistance needed for an acceptable degree of coagulation is less forsmaller diameter filaments and lower flow velocities. The ratio of thecoagulation distance to the exit/entrance flow field diameter ispreferably in the range of about 5 to about 100 and more preferably inthe range of from about 10 to about 20. The NT filaments are combined atthe combining nozzle 18 to produce a NT multifilament 19.

[0063] Due to the strong extensional flow applied in the contained flownozzle of FIG. 5, the diameter of the coagulated NT filament istypically much smaller that that produced in the known versions of theCS process. Although the contained flow filament has higher strength perunit of cross-sectional area, the overall-breaking load of the filamentis smaller and subsequent handling of a monofilament is difficult. Insuch cases, it is customary to handle fine fibrous materials as yams toincrease the breaking load by a factor approximately equal to the numberof monofilaments in the yam cross-section.

[0064] Since electrochemical applications of carbon nanotubes asactuators, supercapacitors, energy harvesting devices, and hydrogenstorage devices require high surface area, the extremely high densityreported for CS spun fibers (Bernier et al., talk Tue E1 at theInternational Conference on Science and Technology of Synthetic Metals,Gastein, Austria, Jul. 15-21, 2000) suggests that these applicationswould be impossible for the CS derived nanotube fibers. Consequently, weunexpectedly discovered that coagulation spun HiPco NTs provide robustelectromechanical actuation after they have been thermally annealed.

[0065] Electrochemical actuation of coagulation spun and annealed fibersis shown in FIG. 2 and described in more detail in Example 7. FIG. 2ashows plots of actuator strain for an thermally annealedcoagulation-spun SWNT fiber in 1 molar NaCl aqueous solution duringchanges in the applied voltage (versus saturated calomel electrode, SCE)and charging current. The applied voltage (versus SCE) is ±1 volt. FIG.2b shows the generated stress versus the peak-to-peak of the appliedvoltage (symmetrically measured about 0 voltage on the SCE scale). Thisis the first demonstration of significant electromechanical actuationfor a carbon nanotube fiber of any sort. This discovery enables a rangeof applications based on the application of carbon nanotubes in liquidelectrolytes, which require a high surface area.

[0066] Actuator devices, supercapacitor, energy harvesting and relatedelectrochemical devices based on carbon nanotubes are described byBaughman et al. in Science 284, 1340-1344 (1999) and in a copendingpatent application. Also, Tennent et al. have described in U.S. Pat. No.6,031,711 the application of sheets of carbon nanotubes as highperformance supercapacitors. FIG. 9 shows a double layerelectromechanical actuator that also functions as a supercapacitor. Eachof these devices comprise at least two electrodes, 20, 21 at least oneof which comprises carbon nanotubes, and at least one electrolyte.Various electrolytes can be used for applying the annealed nanotubefibers, ribbons, and yarns in electrochemical devices, includingactuators, supercapacitors, and devices for harvesting electricalenergy. Very high ionic conductivity electrolytes (like concentratedaqueous KOH and sulfuric acid) are preferred for devices that providethe most rapid responses. Aqueous electrolytes comprising at least about4 M aqueous H₂SO₄ or 4 M aqueous KOH are especially preferred. Aqueouselectrolytes comprising about 38 weight percent H₂SO₄ and electrolytescomprising above 5 M aqueous KOH are most especially preferred. Forcases where a large device response range is more important than deviceresponse rate, electrolytes with large redox windows are preferred,since an increased voltage range increases the achievable deviceresponse range. Most preferred organic electrolytes include propylenecarbonate, ethylene carbonate, butylene carbonate, diethyl carbonate,dimethylene carbonate, and mixtures thereof with salts such as LiClO₄,LiAsF₆, LiPF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, and Li(CF₃SO₂)₃C.

[0067] Solid-state electrolytes can also be used advantageously, sincesuch electrolytes enable all-solid-state devices. More preferredorganic-based solid-state electrolytes are polyacrylonitrile-based solidpolymer electrolytes (with salts such as potassium, lithium, magnesium,or copper perchlorate, LiAsF₆, and LiN(CF₃SO₂)₂). More preferred organicsolvents for these solid-state and gel electrolytes include propylenecarbonate, ethylene carbonate, γ-butyrolactone, and mixtures thereof.Preferred gel or elastomeric solid electrolytes include lithiumsalt-containing copolymers of polyethylene oxide (because of high redoxstability windows, high electrical conductivities, and achievableelastomeric properties), electrolytes based on the random copolymerpoly(epichloridrin-co-ethylene oxide), phosphoric acid containing nylons(such as nylon 6,10 or nylon 6), and hydrated poly(vinyl alcohol)/H₃PO₄.Other preferred gel electrolytes include polyethylene oxide andpolyacrylonitrile-based electrolytes with lithium salts (like LiCl)₄)and ethylene and propylene carbonate plasticizers. The so called“polymer in salt” elastomers (S. S. Zhang and C. A. Angell, J.Electrochem. Soc. 143, 4047 (1996)) are also preferred forlithium-ion-based actuators, since they provide very high lithium ionconductivities, elastomeric properties, and a wide redox stabilitywindow (4.5-5.5 V versus Li⁺/Li). Preferred electrolytes for hightemperature actuators include ionic glasses based on lithium ionconducting ceramics (superionic glasses) (up to 250° C.), ion exchangedβ-alumina (up to 1,000° C.), CaF₂, and ZrO₂/Y₂O₃ (up to 2,000° C.).Other preferred inorganic solid-state electrolytes are AgI, AgBr, andAg₄RbI₅. Preferred inorganic molten salt electrolytes for hightemperature actuators include alkali metal halides (such as NaCl, KCl,and mixtures of these salts) and divalent metal halides (such as PbCl₂).In some device applications it is desirable to use differentelectrolytes in different parts of the device. For example, theelectrolyte that penetrates the carbon nanotube fiber, ribbon, or yarncan be different from the electrolyte that separates electrodes in theactuator. For instance, the electrolyte within the SWNT fiber can be asolid-state electrolyte that enhances the mechanical stress transferbetween nanotubes, while a liquid electrolyte might be chosen for theinter-electrode space, so that high electrolyte conductivity of thiselectrolyte enhances the achievable rate performance.

[0068] The presently demonstrated ability to spin substantiallyimpurity-free nanotube fibers and ribbons means that these fibers orribbons can be combined (either together or separately) usingconventional fiber technology to make yarns and woven articles. FIG. 10shows a schematic of a typical woven article of ribbons of alignedcarbon nanotubes produced by the improved coagulation spinning processand stabilized by heat treatment. In instances where it is desirable toprovide a setting of the nanotube structure, the annealing to eliminatethe dimensional instability of the as-spun nanotube fibers is preferablyaccomplished after the nanotube fibers, ribbons, or yarns are woven,wound, or otherwise configured into the desiredcarbon-nanotube-containing article.

[0069] Fiber and or ribbons combined as yarns can be used to maximizethe rate performance of electrochemical devices by minimizing theseparation between the two electrodes (working and counter electrodes)that are required for these devices. This utilization of the fibers,ribbons or yams produced by the coagulation spinning process can beaccomplished by the following preferred invention embodiment: (1)impregnate two or more lengths of annealed CS nanotube fiber, ribbon oryarn with a solid-state electrolyte, such as phosphoric acid/poly(vinylalcohol) including a continuous coating over the outer fiber or ribbonsurface; (2) attach a working electrode contact to a fraction of theseelectrolyte-impregnated fibers, ribbons, or yarns, and counter electrodecontacts to the remaining of these electrolyte-impregnated fibers,ribbons, or yarns; and (3) combine these working and counter-electrodenanotube elements (along with electrolyte that ionically connects theseelements) in a geometry appropriate for the particular targeted deviceapplication. Examples of particularly preferred geometries are (a) aparallel, straight array of these elements in which the workingelectrode elements are interdispersed with the counter-electrodeelements, most preferably so as to minimize average separation betweenelectrode elements of different types, and (b) a wound array of theseelectrode elements obtained by winding the two or more electrode lengthssimultaneously or sequentially onto a mandrel, thereby forming a hollowcylindrical body comprising two or more interpenetrating electrodes ortwo or more layered electrodes. For another preferred geometry, the twoor more lengths of electrolyte impregnated and coated NT fiber, ribbonor yarn may be woven into a cloth comprising two or moreinterpenetrating electrodes. Electrical connections can be convenientlymade in various ways, such as by weaving working and counter electrodeelements in orthogonal directions in a woven cloth, so that separateelectrical connections can be separately made and maintained for thesedirections.

[0070] These thereby configured electrode elements comprising carbonnanotube fibers, ribbons, or yarns can be used as various types ofelectrochemical devices. The most preferred of these devices areactuators and supercapacitors. Such use of nanotube fibers, ribbons, andyarns enables the multifunctional application of carbon nanotubes. Forexample, a soldiers vest woven from the above-described cloth could beused to provide both a structural function and an energy storagefunction (supercapacitor).

[0071] The unannealed CS spun filaments are can be more supple than theyare in the heat treated state (especially if the unannealed fiberscontain absorbed water) and in some cases it is found advantageous topostpone the annealing step until after winding, weaving or other lay-upsteps. In this case, the electrolyte must be placed within the porousstructure after heat treatment and insulating separators must beincorporated within the wound or woven structures. Such separators maycomprise layers of glass or ceramic fiber or yarn wound or woven betweenthe NT fibers. As in the case of the as spun fiber, ribbons, or yams,the annealing temperature for wound or woven objects is preferably inthe range of between about 200° C. and about 2100° C. and morepreferably in the range of between about 400° C. and about 1200° C. Insome cases the annealing step is advantageously carried out with thewound body or woven cloth in a state of tension. In this way, aclosed-end wound cylindrical shell can be annealed using internalpressure to create a state of tension in the shell.

[0072]FIG. 11 shows a schematic of a wound article of ribbons of alignedcarbon nanotubes produced by the improved coagulation spinning processand stabilized by heat treatment. Carbon nanotubes 22 are wound around amandrel 23. The wound structure 24 can be removed from the mandrel 23either before or after heat treatment.

[0073] The nanotube structure of the invention can be utilized for thestorage of gases such as hydrogen. Carbon nanotubes are known to storehydrogen efficiently (M. S. Dresselhaus et al., MRS Bulletin 24, 45-50(1999)) and the fiber or ribbon geometry is good for this applicationbecause it keeps the nanotubes in place (i.e., the nanotubes don't flyout with the hydrogen when the hydrogen is withdrawn from the storagevessel). The gas storage system can be an annular nanotube body made bywinding the nanotube fiber or ribbon on a mandrel. This annular bodywould be contained in a cylindrical pressure vessel with a gasinlet/outlet port. An external or internal heater would be used fordesorbing the stored gas.

[0074] The actuators enabled by the fibers, ribbons, and yams of thisinvention may be used for the conversion of electrical energy tomechanical energy. The applications for these mechanical actuators arediverse and include, for example, robotic devices; high temperature airflow valves for aircraft engines; optical switches for optical fiberinterconnects; adjustable structures for vibration suppression andfailure avoidance; phase shifters for optical gyroscopes; precisionelectronic gyroscopes; and artificial muscles for space suits. Theseelectromechanical actuators resulting from invention embodiments canprovide (a) high-stress-generation capabilities, (b) high gravimetricand volumetric work capabilities per cycle, and (c) high volumetric andgravimetric power generation capabilities. Also, the actuators of thepreferred embodiments can operate at low voltages, which providessavings in device electronics, avoids potential safety hazards, andminimizes electromagnetic interference effects.

[0075] The carbon nanotube fibers of invention embodiments can also beused for carrying high currents. This capability to carry high currentsresults from the combination of their reasonably high electricalconductivities and their high thermal conductivity and high thermalstability (enabling substantial heating and conduction of produced heatfrom the fibers). The invention embodiments that provides the NT fibersof this invention as windings on a mandrel (with optional heat set onthe mandrel) enables a preferred use of the carbon nanotubes as motorwindings, electromagnet windings, and the winding for transformers.

[0076] The following examples are provided to more particularlyillustrate the invention, and should not be construed as limiting thescope of the invention.

EXAMPLE 1

[0077] This example demonstrates the successful use of coagulationspinning to produce long SWNT filaments that are substantially impurityfree. The utilized HiPco nanotubes were made by the high-pressure carbonmonoxide route described by R. E. Smalley et al. in InternationalApplication No. PCT/US99/25702. Characterization of this material byRaman spectroscopy showed a nanotube diameter of about 0.84 nm. A 15 gquantity of nanotube mixture, which contains 0.4% (0.060 g) of the HiPcoSWNTs and 1.2% (0.18 g) surfactant in 98.4% (14.76 g) distilled waterwas prepared. The surfactant used was sodium dodecyl sulphate (SDS151-21-3, purchased from ICN Biomedical, Aurora Ohio). The mixture wassonicated for about 15 minutes by BRANSON MODEL 350 20 kHz sonifier,purchased from Branson Ultrasonic Corporation, Danbury Conn. Sonicationof the NT/surfactant/water mixture was accomplished in a 21 cc glassbottle (25 mm inside diameter), which was placed in a cold water bath inorder to minimize sample heating during ultrasonication. The sonication(using the 12.7 mm diameter ultrasonic horn with the standard flat tip)was accomplished by inserting the tip of the sonicator a centimeter deepinto the NT/surfactant/water mixture. The output control of the abovesonifier was set to 3; the mode of operation was set to pulsed with thesetting 0.7 sec on/0.3 sec off; the process timer was set to 15 min andthe total estimated input power was 30 watts. The sonication stepproduced a stable, homogeneous colloidal suspension. For use as acoagulation bath, a 5% by weight solution of poly(vinyl alcohol) (PVA)was prepared by combining 50 g of Fluka PVA (molecular weight 49000,catalogue No 8138) with 950 g of distilled water, heating to 70° C. andmixing for about 2 hrs. This PVA solution was placed in a glass cylinder(100 mm in diameter and 50 mm high and fixed concentrically on rotatingtable. A stainless steel needle was used for injecting the spinningsolution into the coagulation bath. This needle (purchased from Popper &sons, Inc., Cat. No. 7181, measuring 150 mm long, 0.80 mm O.D., 0.50 mmI.D.) was ground to obtain a flat and perpendicular exit end. Theinjection needle was bent so that the spinning ink could be injectedparallel to the bath surface. The point of injecting the spinning inkwas at a radius of 35 mm from the center of the cylindrical dish, about10 mm under the surface of the PVA solution, and parallel to the dishbottom. The glass cylinder containing the PVA solution was rotated at 30rpm. The employed rate of 1.67 ml/minute for injecting the spinningsolution into the coagulation bath was achieved using a Model 200 seriesKD Scientific syringe pump with a 10.25 mm I. D. syringe. After laminarrotational flow was established, the syringe pump was activated andnanotube solution injected in a direction parallel to the establishedflow. The coagulation of nanotubes from the nanotube solution formed acontinuous spiral ribbon inside the PVA solution. The ribbon wassubsequently washed in water and dried in air to form nanotubefilaments. The details of fiber washing and drying are as follows: Theribbon was carefully transferred from the PVA solution into a bath ofdistilled water and left there for 2 hrs with no stirring or agitation.This procedure was repeated five times, each time using a fresh bath ofwater. The washed ribbon was then attached to a metal hook and pulledout of the water at a rate of about 200 mm/hr. The resulting driednanotube filament was essentially round in cross-section, with adiameter of about 0.050 mm.

EXAMPLE 2

[0078] The CS process of Example 1 was unsuccessful when the SWNTs usedfor the spinning solution were highly purified SWNTs obtained by thepurification of carbon-arc-synthesized nanotube-containing soot. Thesepurified carbon nanotubes were obtained from CarboLex, Inc, Universityof Kentucky, Lexington Ky. The nanotube suspension was prepared,sonicated and spun exactly as in Example 1. The spinning did not resultin the formation of continuous ribbons or filaments. Rather, theinjected stream of nanotube suspension broke up into short lengths uponinjection into the PVA bath.

EXAMPLE 3

[0079] The CS process of Example 1 was unsuccessful when the SWNTs usedfor the spinning solution were highly purified SWNTs obtained by thepurification of laser-evaporation produced nanotube-containing soot.These chemically purified carbon nanotubes were purchased fromtubes@rice, Rice University and consisted predominately of nanotubeshaving a diameter of about 1.2 to 1.4 nm. The nanotube suspension wasprepared, sonicated, and spun exactly as in Example 1. The spinning didnot result in the formation of continuous ribbons or filaments. Rather,the injected stream of nanotube suspension broke up into short lengthsupon injection into the PVA bath.

EXAMPLE 4

[0080] The CS process of Example 1 was unsuccessful when the SWNTs usedfor the spinning solution were chemically purified SWNTs obtained by thepurification of material synthesized by catalytic decomposition ofmethane at 1000° C. over well-dispersed metal particles supported onzeolite. The nanotube suspension was prepared, sonicated and spunexactly as in Example 1. The spinning did not result in the formation ofcontinuous ribbons or filaments. Rather, the injected stream of nanotubesuspension broke up into short lengths upon injection into the PVA bath.

EXAMPLE 5

[0081] The following provides a further example of the spinning ofcarbon nanotubes that are substantially free of carbonaceous impuritiesand have outstanding modulus and strength compared with prior-artnanotube fibers. The obtained modulus (25 GPa) is about 25 times higherthan normally obtained for sheets of carbon nanotubes and about twicethe highest modulus of carbon nanotube fibers spun by the prior-arttechnology. One reason for this major improvement in mechanicalproperties is believed to be the present use of a special spinningnozzle that is designed to increase nanotube alignment in the spunfibers. Except for the following features, the spinning solution andspinning method were the same as for Example 1. As an improvement on theprocess of Example 1, following sonication, the spinning solution wasfiltered twice through two layers of metal mesh that had a 25 mmdiameter and 0.025 mm openings. The advantage of using this filtrationprocedure was to eliminate non-dispersed clumps of nanotubes thatsurvived the sonication process, which produced occasionalirregularities in the fiber produced in Example 1. In addition, ashear-flow injection nozzle with conical cross-section (see FIG. 4) wasfitted over the end of the injection needle. The part of the nozzle incontact with solution had the following dimensions: a 0.84 mm entrancediameter, a 0.38 mm exit diameter, and a 7.62 mm length. Other changesfrom Example 1 were as follows: The coagulation was rotated at a higherrate of 50 rpm, and the washing of the coagulated ribbon was for 16hours in a bath of distilled water. The dried fiber drawn from the waterbath was essentially round and had a cross-sectional diameter of 0.03mm. The measured modulus of the dry fiber was 25 GPa, the ultimatestrength at break was 273 GPa, and the strain to break was about 6%.

EXAMPLE 6

[0082] This example demonstrates the instability of as-spun fibers in anaqueous electrolyte and the use of thermal annealing to eliminate thisinstability. It also demonstrates the high extensional elastic modulusof fibers coagulation spun from HiPco nanotubes, compared to highquality bucky paper (whose elastic modulus is typically about 1 GPa).The fiber was spun from aqueous suspension containing 0.4% nanotubes and1.2% SDS by the process described in Example 1. After spinning, thefiber was washed in water and dried by slow pulling from the water bath.The cross-sectional area of the prepared fiber ranged from 0.0005 to0.0026 mm² as determined by optical microscopy. The heat treatment ofthe material was performed in a titanium gettered flowing argonatmosphere tube furnace at a temperature of 1080° C. for 1 hour.Measurements of the stress-strain dependencies and Young modulus werecarried out at ambient conditions using a Seiko Instruments Dynamic LoadThermomechanical Analyzer TMA/SS120C. Two runs were taken on the samefiber for both as prepared and annealed materials. First, the fiber wastested in air and the data on dry modulus were obtained. Then the fiber,while still attached to the TMA sample holder, was put in deionizedwater, kept wet for 10 minutes and measured for a second time. Thesecond run provided data on wet modulus. The results of the measurementsare summarized in Table 1. TABLE 1 Modulus results. Material Dry Modulus(GPa) Wet Modulus (GPa) As prepared fiber 16.8 0   Annealed fiber 11.27.1

[0083] The as-prepared fiber readily absorbs water and swells to severaltimes its dry state diameter. Because of the swelling in wet state thefiber elongates and looses its integrity under any minor load. The wetmodulus for the as-prepared fiber was below the sensitivity of ourmachine and is close to zero. The thermal annealing eliminated theswelling that resulted in this essentially complete loss of modulus inwater or in an aqueous electrolyte. Annealing of the as-spun fibers at100° C. for one hour did not eliminate swelling in fiber diameter andthe loss of mechanical properties when the fibers were immersed inwater. These 100° C. annealed fibers doubled in diameter when immersedin water. However, annealing the as-spun fibers at 200° C. for one hourresulted in annealed fibers that changed diameter by less than 10% whenimmersed in water.

EXAMPLE 7

[0084] This example illustrates the typical electromechanical response(force generation capability) of thermally annealed, coagulation-spunnanotube fiber in aqueous 1 M NaCl electrolyte. This response shows thatthese thermally annealed, coagulation-spun fibers can be used inactuator applications, and in other electrochemical applications thatrequire a high surface area. Because of the instability of prior-art CSnanotube fibers, these fibers could not be used for electrochemicalapplications. The fiber used for testing was prepared by the spinningprocess described in Example 1 and annealed at 1080° C. temperature asoutlined in Example 6. The cross-sectional area of the fiber determinedby optical microscopy was equal to 0.0013 mm². Theelectrochemically-generated force in these fibers was measured using asensitive force transducer similar to the one used in a high precisionanalytical balance. The measured force change was normalized by thecross-sectional area of fiber to provide the actuator-generated stress.The fiber (attached to an arm of the force transducer) was put inaqueous 1 M NaCl solution, stretched under a constant stress of 4 MPaand subjected to a periodic potential at a frequency of 0.03 Hz. Thepotential (measured versus saturated calomel electrode, SCE) was asquare wave potential, which was applied using a Gamry Instruments PC4Potentiostat. The nanotube fiber and a Pt mesh acted as the working andcounter electrodes, respectively. The typical electromechanical responseof the fiber, recorded at voltage amplitude of 1V vs SCE, is shown inthe left panel of FIG. 2. The response follows the waveform of theapplied electric potential with a stress amplitude of 2.1 MPacorresponding to a potential change of 2V (from 1V to −1V). The stressamplitude was found to be proportional to the voltage amplitude with theslope of the dependence being about 0.9 MPa/V, as shown in the rightpanel of FIG. 2.

EXAMPLE 8

[0085] This example illustrates the dramatically increased range ofspinable compositions that result for the invention embodimentsemploying the HiPco nanotubes. As shown in FIG. 3, it was possible tospin fibers over the nanotube composition range of at least 0.2 to 0.5%and surfactant concentrations between as least as low as 0.6% to atleast as high as 3%.

[0086] It is to be understood that the foregoing descriptions andspecific embodiments shown herein are merely illustrative of the bestmode of the invention and the principles thereof, and that modificationsand additions may be easily made by those skilled in the art withoutdeparting for the spirit and scope of the invention, which is thereforeunderstood to be limited only by the scope of the appended claims.

What is claimed is:
 1. A process of making a structure containing carbonnanotubes which comprises: forming a uniform suspension of carbonnanotubes in a liquid; coagulation spinning the suspension to form thestructure; and annealing the structure at an annealing temperature ortemperatures sufficient to stabilize the structure against swelling andloss of mechanical strength upon immersion in water or other liquid. 2.The process of claim 1, wherein the structure is a fiber, ribbon oryarn.
 3. The process of claim 1, wherein the water or other liquid isused as a component of an electrolyte.
 4. The process of claim 1,wherein the maximum annealing temperature is between about 200° C. andabout 2100° C.
 5. The process of claim 1, wherein the maximum annealingtemperature is between about 400° C. and about 1200° C.
 6. The processof claim 1, wherein the carbon nanotubes comprise single-wall carbonnanotubes.
 7. The process of claim 6, wherein the average diameter ofthe single-wall carbon nanotubes is in the range of about 0.6 nm toabout 0.9 nm.
 8. The process of claim 6, wherein the carbon nanotubes inthe suspension are made at high pressure from carbon monoxide, thenanotubes being free of carbonaceous contaminants.
 9. The processaccording to claim 6, wherein a diameter distribution of the carbonnanotubes is bimodal with a first peak centered in the range of about0.6 nm to about 0.9 nm and a second peak at a larger diameter in therange of about 1.0 nm to about 2.0 nm.
 10. The process of claim 1,wherein the annealing is performed after a step of weaving or windingthe structure.
 11. The process of claim 1, wherein the annealing isperformed while the structure is under a state of tension.
 12. Theprocess of claim 11, wherein either the tension is between about 10 MPato about 300 MPa or the structure is maintained at substantiallyconstant length.
 13. The process of claim 1, wherein the annealing isperformed in inert or reducing atmosphere and a maximum annealingtemperature is above about 600° C.
 14. The process of claim 1, whereinthe annealing is performed in an atmosphere of steam.
 15. The process ofclaim 1, wherein the step of coagulation spinning is performed using ashear-flow-inducing nozzle.
 16. The process of claim 1, wherein thesuspension of carbon nanotubes comprises a surfactant, water, andnanotubes synthesized by metal-particle-catalyzed disproportionation ofcarbon monoxide.
 17. The process of claim 16, wherein the surfactant issodium dodecyl sulfate.
 18. The process of claim 1, wherein thecoagulation spinning occurs in a polymer containing solution.
 19. Theprocess of claim 18, wherein the polymer in the polymer containingsolution is poly(vinyl alcohol).
 20. A coagulation spun structurecomprising single-wall carbon nanotubes, the structure swelling by lessthan about 10% in diameter when immersed in water.
 21. The structure ofclaim 20, wherein the structure comprises fiber, ribbon or yarn.
 22. Thestructure of claim 20, wherein the single-wall carbon nanotubes have anaverage diameter in the range of about 0.6 nm to about 0.9 nm
 23. Thestructure of claim 20, wherein the structure further comprises anelectromechanical actuator, a supercapacitor or a woven article.
 24. Thestructure of claim 21, wherein the fiber, ribbon, or yarn forms awinding on a mandrel.
 25. The structure of claim 20, wherein thestructure forms a main hydrogen storing element for a hydrogen storagedevice.
 26. A fiber, ribbon or yarn comprising greater than about 90weight percent carbon single-wall nanotubes, wherein average diameter ofthe single-wall carbon nanotubes is about in the range of about 0.6 nmto about 0.9 nm.
 27. A fiber comprising single-wall carbon nanotubes,the fiber containing no binding agent or carbonaceous impurities.
 28. Aprocess of coagulation spinning of a fiber, ribbon, or yarn, whichcomprises: providing a first liquid comprising a uniform dispersion ofsingle-wall-carbon nanotubes; and injecting the first liquid as a jetinto a second coagulation liquid, the jet being formed in an orifice ofdecreasing diameter, which creates a converging flow field at close tothe point of injection into the second coagulation liquid.
 29. Theprocess of claim 28, wherein the jet is formed in an orifice which has across section that is neither round, elliptical, square, or rectangular.30. The process of claim 28, wherein the jet is injected from a tubularchannel of decreasing diameter into an annular stream of the secondcoagulation liquid that flows coaxial with and surrounding the jet. 31.The process of claim 30, wherein a major proportion of the coaxiallyflowing coagulation solution is removed through a section of porous wallflow tube located downstream of the converging flow field.
 32. Theprocess of claim 31, wherein two or more liquid streams, which eachcontain a nanotube structure in the coagulation liquid, are combinedinto a single flow stream containing two or more nanotube structures.33. The process of claim 28, wherein the carbon nanotubes are free ofcarbonaceous impurities and the average diameter of the single-wallcarbon nanotubes is in the range of about 0.6 nm to about 0.9 nm. 34.The process of claim 28, wherein the second coagulation liquid containsa polymer.
 35. The process of claim 34, wherein said polymer ispoly(vinyl alcohol).
 36. The process of claim 28 that further includesannealing the fiber, ribbon, or yarn at a maximum annealing temperatureof between about 200° C. to about 2100° C.